Free piston engine starting system



June 20, 1961 FALBERG 2,988,873

FREE PISTON ENGINE STARTING SYSTEM Filed May 29, 1958 United States Patent Ofilice 2,988,873 Patented June 20, 1961 2,988,873 FREE PISTON ENGINE STARTING SYSTEM Robert F. Falberg, Birmingham, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed May 29, 1958, Ser. No. 738,801 3 Claims. (CI. 60-44) This invention relates to the starting of free piston engines, gasifiers and compressors. The invention relates more particularly to an improved arrangement for isolating dual free piston gas generators after they have been started.

Where two or more free piston gas generators are em ployed to supply gas under pressure to a power conversion device such as a turbine, it is desirable to run the gas generators out of phase to provide a more uniform gas discharge. During starting of the generator however, it is more suitable to have the units connected so as to be in phase. It is therefore desirable to provide an automatic valve to isolate the engines by breaking the connection between the two engines after they have been started, and one such arrangement is shown in co-pcnding application S.N. 584,744 by Warren H. Smith, filed May 14, 1956 now Patent No. 2,839,911, issued June 24, 1958. The arrangement shown in said Patent No. 2,839,911 utilizes air box pressure to operate the isolating valve. In a fully automatic starting system utilizing alternate suction and pressure to maneuver the pistons, such as that shown in my co-pending application S.N. 620,972, filed Nov. 7, 1956, now Patent No. 2,956,396, issued Oct. 18, 1960, it is desirable to provide a system having an automatic isolating valve controlled by the alternative suction and pressure that is both simple and effective. This invention relates to such a starting system employing such an automatic isolating valve.

It is therefore an object of this invention to provide a free piston engine starting system having an automatic isolating valve for connecting two or more independent gasifier units during starting and to isolate the units after the starting operations have been completed.

This and other objects and advantages of the invention will be readily apparent from the following specification and drawings which illustrate a preferred embodiment of the invention but which are not to be consid cred as limiting the invention.

The preferred embodiment of the invention comprises a diaphragm operated valve that normally isolates the cushion chambers of independent free piston units but is actuated to connect the chambers either by vacuum utilized to move the compressor pistons to their outer positions or by positive pressure utilized to move the pistons inwardly. The valve is effective also to connect the maneuvering vacuum or pressure to the individual cushion chambers only during the starting procedure.

Referring to the drawings, FIGURE 1 is a diagrammatical sectional view of a dual free piston machine;

FIGURE 2 is an enlarged cross-sectional view of the isolating valve employed in the invention; and

FIGURE 3 is a cross-sectional view taken on the line 33 of FIGURE 2.

FIGURE 1 of the drawings diagrammatically shows a gas turbine free piston machine that could be used as a gasifier for providing a continuous supply of gases under high pressure and temperature to a prime mover such as a gas turbine; also the machine could be adapted for use as a gas compressor or for other purposes.

The engine includes a case or housing 1, a portion of which defines two motor cylinders 3 in which are reciprocably mounted opposed motor pistons 5. Each motor cylinder 3 has inlet ports 7 and exhaust ports 9 at opposite ends of the cylinder.

These ports are opened and closed by the motor pis tons 5 which are rigid with large compressor pistons 11 adapted to reciprocate in cylinder 13 also formed by th. engine case 1. Each compressor cylinder has an inle port 15 controlled by a valve 17 normally urged to closer position by a spring 19. Each compressor cylinder alsr has an exhaust port 21 controlled by a valve 23 normall: closed by a spring 25. The opposed movable masses 0 the pistons 5 and 11 of each unit are kept in proper rela tionship with each other by a separate synchronizing link age, not shown, which may be of any known type, to example that shown in my co-pending application S.N 620,972 referred to above. The upper and lower individ ual units are designated by A and B, respectively, in FIG URE 1.

The two units of the engine are operated by know: supercharged two stroke diesel engine principle. Initia movement of the movable masses 511 towards eacl other causes entrapment of supercharged air and furthel compression of this air in the motor cylinders 3. A the proper time fuel is injected by known means, not forming part of the invention, but which may be sucl as that shown in Patent No. 2,811,958. The fuel injected into the compressed air between the motor piston: is ignited by the heat of compression. The increase ir pressure created by the burning fuel acts on the opposec' faces of the motor pistons 5 and forces the movable face: 5-11 away from each other.

Each compressor cylinder 13 is divided by the com pressor piston 11 into a compression chamber 14 and cushion or rebound chamber 16. As the movable masses 511 move outwardly their motion is checked by air entrapped in the cushion chamber 16, which then possesses practically all the energy developed by the motor cylinder 3 and restores this energy to the movable masses 511 during the next inward stroke. Motor cylinders 3 are scavenged by air which is drawn in past the inlet valves 17 during outward movement of the masses 511, compressed in chamber 14 during the inward stroke ol the masses 511, and delivered past the discharge valves 23 into the case chamber 20. A connecting passage 22 equalizes the pressure on the respective chambers 20 of the units A and B. On the next outward stroke of the masses 5-11, compressed air in chamber 20 enters the motor cylinder 3 through inlet ports 7 and travels through the motor cylinder 3 and out exhaust ports 9 into an exhaust collector 27 and then to some power generating device such as a gas turbine.

The rebound chambers 16 of unit A are connected together by a passage 28 to equalize the pressures in the opposite chambers. The cushion chambers 16 of unit B are similarly connected together by a stabilizer S, of any known type, for example that shown in US. Patent No. 2,355,924. The stabilizer, which forms no part of this invention, operates only after the starting cycle is completed.

The starting system in the preferred embodiment comprises a unidirectional pump P having a pressure dis charge passage 29 and a suction passage 31 leading to a positioning control valve E, the details and operation of which are fully described in my co-pending application S.N. 620,972 referred to above. The positioning control valve E acts to connect either the discharge passage 29 or the suction passage 31 to a starting pressure passage 33 that leads to an isolating valve C. It is understood that a bi-directional pump may be utilized to provide the suction and positive pressures for maneuvering the pistons. In such a system the direction of rotation of the pump is reversed to change from suction to positive pressure. Similarly two pumps, one a vacuum and one a positive pressure pump, could be alternately connected to passage 33.

The isolating valve C, seen in detail in FIGURES 2 and 3, comprises a valve body 39 having a reciprocating valve member 41 connected to a rod 43 that is attached to a flexible diaphragm 45. The outer periphery of the diaphragm 45 is held between cover members 47 and 49. Chamber 37 is always connected to the atmosphere by hole 55. The diaphragm and the covers act to form two chambers 37 and 38. A pair of springs 51 and 53 normally hold the diaphragm in its center position thereby holding the valve member 41 in the position shown in FIGURE 2. The valve body 39 has three radially drilled holes 59, 60 and 61. Hole 59 forms a port connected to a pipe 63 leading to the cushioning chamber 16 of unit A, and hole 61 similarly forms a port connecting with a pipe 65 leading to the cushion chamber 16 of unit B. The third hole 60 forms a port connected with the starting fluid passage 33 leading from the positioning control valve E.

A connecting passage 57 continually connects the chamber 38 with the passage 33 so that whatever pressure exists in passage 33 will exist in chamber 38. A drilled hole 67 in the valve member 41 acts to connect the chambers on either side of the valve member 41.

Operation Operation of the starting system is as follows: Valve E is initially in a position to connect the suction passage 31 with the pipe 33 and when the pump P is operated a vacuum will be created in passage 33 and by means of connecting hole 57 in the valve C, a vacuum will be created in chamber 38. Atmospheric air pressure entering chamber 37 through the hole 55 will act on the diaphragm to move it and the rod 43 against the spring 53 thereby moving the valve member 41 to the right to connect the passage 33 with the pipes 63 and 65. As the pump P continues to operate, air is drawn out of the cushion chambars 16 and when the pistons have moved to their outermost positions, mechanisms, of known type and not shown, but which may be of the type shown in my abovementioned application S.N. 620,972, acts to operate the positioning control valve E to connect the discharge or pressure passage 29 with the pipe 33. 1

With passage 33 no longer having a vacuum, dilierential pressure no longer acts on diaphragm 45 and spring 53 returns the diaphragm and valve 41 to its position of FIGURE 2 blocking passages 33, 63 and 65 from each other. Valve E now directs positive pressure into pipe 33 and by means of passage 57 acts on diaphragm 45 to move it and valve 41 to the left against spring 51. Passages 63 and 65 are then connected with pipe 33 and the fluid under pressure flows to chambers 16 to act on pistons 11. A latching or holding mechanism, not shown and of known type, such as that shown in my application S.N. 620,972, holds the masses 5-11 in an outer position until a predetermined pressure exists in chambers 16. The latching mechanism then is released and masses 5-11 allowed to move inwardly by the high pressure in chambers 16. The pump P is automatically stopped when the latch mechanism releases the masses 5-11 and with absence of pressure from the pump and with the expansion of the pressure in chambers 16, the compressed spring 51 returns diaphragm 45 and valve 41 to their neutral position of FIGURE 2 sealing off passages 63 and 65 from each other and from passage 33 during the running of the gasifier.

The invention provides an improved control apparatus suitable for use in many applications in the art of free piston machine control and the principles of the invention may be utilized in other arts through the use of ordinary skill.

It will be apparent to those skilled in the art that modications of the system and components thereof may be made within the scope of the invention which is not to be considered as limited by the detailed description of the embodiment shown.

I claim:

1. A free piston power plant comprising, in combination, a pair of independent free piston units each including a first cylinder and piston means defining a power cylinder, and a second cylinder and piston means defining a compressor cylinder having a compressor chamber and a rebound chamber, means operatively connecting said first piston means and said second piston means, first and second conduits each connected to one of said rebound chambers, valve means between said conduits having a normally closed condition isolating the conduits from each other and an open condition connecting said rebound chambers with each other and with a third conduit, an air starter pump having a pressure discharge conduit and a suction conduit, means for alternatively connecting said third conduit with said discharge conduit or said suction conduit, closing means for moving said valve means to its closed condition, and valve operating means operatively connected to said valve means to open the same and connect said first, second and third conduits with each other, said valve operating means responsive to operation of said starter pump to open said valve and responsive to cessation of operation of said pump to allow said closing means to move said valve to its closed condition to disconnect said first, second and third conduits.

2. A starter system for a free piston power plant having a plurality of individual independent power units each having a power cylinder and a compressor cylinder interconnected together and a power piston and a compressor piston interconnected together and movable in said respecspective cylinders and a rebound chamber formed by said compressor cylinder and said compressor piston, the combination including rebound conduits leading to each of said rebound chambers arranged to supply air to or exhaust air from said chambers, a starter means for supplying air under pressure to or exhausting air from a starter conduit, a three position valve between said rebound conduits and said starter conduit, said valve having a first normal position wherein said rebound conduits are disconnected from each other and "from said starter conduit, and second and third positions wherein said conduits are connected to each other and to said starter conduit, and means connected to said valve to normally move said valve to said first position and responsive to operation of said starter means for supplying air to said starter conduit to move said valve to said second position and responsive to operation of said starter means to exhaust air from said starter conduit to move said valve to said third position 3. A free piston power plant comprising, in combination, two independent free piston units each including a power cylinder and a compressor cylinder interconnected together and a power piston and a compressor piston interconnected together and movable in said respective cylinders and a rebound chamber formed by said compressor cylinder and said compressor pistion, means to establish dephased operation of said power units, first and second conduits each connecting to the rebound chamber of one of the units, a starter arranged to alternatively provide positive presure air to or evacuate air from a third conduit, a normally closed valve between said first, second and third conduits, said valve having an open condition connecting said first, second and third conduits to each other and a closed condition isolating said first, second and third conduits from each other, and means responsive to positive pressure on to negative pressure in said third conduit connected to said valve to move the valve to said open position.

Huber June 18, 1957 Smlth June 24, 1958 

